I picked up older sig P320 slide and barrel thinking all I need is a FCU. Bought a new FCU with the dis-connector, did not know at time. But I have the slide without the dis-connector cut or pre recall I assume. I have another older P320 that is Pre recall without the dis-connect or cut slide and discovered the difference, learning experience. Question is can I make the new FCU work on the older slide? Or can I modify the FCU to work? Or can I find a pre recall FCU?

Give Sig a call. I believe they will still make the proper mod to the older slides gratis. Turn around was really quick for me too.

^^^THIS is your best bet!

Re: your questions:

Can I make the new FCU work on the older slide? No
Or can I modify the FCU to work? No
Or can I find a pre recall FCU? Maybe, but unlikely!

I've never seen anyone parting out a Pre 'Voluntary Upgrade' FCU, though you might be able to find a complete Pistol...YMMV

Great advise to call SIG, shipping out today...thanks